The present invention relates to a fuser that is used in an electrostatic recording type image forming apparatus such as a copying machine, a facsimile, and a printer. More specifically, the invention relates to a heating device and a fuser utilizing electromagnetic induction.
In recent years, in image forming apparatus such as printers, copiers, and facsimiles, market requirements about the energy consumption and the processing speed have become higher. To attain performance that meets those requirements, it is important to increase the thermal efficiency of fusers that are used in image forming apparatus.
In image forming apparatus, an unfused toner image is formed on a recording medium such as a recording sheet, printing paper, photosensitive paper, or electrostatic recording paper by an image transfer type or direct type image forming process such as xerography, electrostatic recording, or magnetic recording. Fusers of contact heating types such as a heat roller type, a film heating type, and an electromagnetic induction heating type are widely employed as fusers for fusing an unfused toner image.
JP-A-8-22206 proposes an electromagnetic induction heating type fuser that utilizes a technique of causing a magnetic metal member as a heating member to generate heat (Joule heat) by electromagnetic induction, that is, by creating eddy current in the magnetic metal member by an AC magnetic field generated by an exciting coil as an induction heating means.
The AC magnetic field generated by the energized exciting coil is not uniform over the entire range and hence the heat generation of the heating member may not be uniform.
This may cause toner fusing unevenness and deteriorate the printing quality.